Poly (alkylene carbonate) is an easily biodegradable polymer and is useful for packaging or coating materials, etc. A process for preparing poly(alkylene carbonate) from an epoxide compound and carbon dioxide is highly eco-friendly because there is no involvement of harmful compounds like phosgene and adopt easily available and inexpensive carbon dioxide.
Since 1960's, many researchers have developed various types of catalysts to prepare poly(alkylene carbonate) from an epoxide compound and carbon dioxide. Recently, we have developed a highly active and highly selective catalyst synthesized from the salen [Salen: ([H2Salen=N,N′-bis(3,5-dialkylsalicylidene)-1,2-ethylenediamine]-type ligand with quaternary ammonium salts [Bun Yeoul Lee, KR Patent No. 10-0853358 (Registration date: 2008.08.13); Bun Yeoul Lee, Sujith S, Eun Kyung Noh, Jae Ki Min, KR Patent Application No. 10-2008-0015454 (Application date: 2008.02.20); Bun Yeoul Lee, Sujith S, Eun Kyung Noh, Jae Ki Min, PCT/KR2008/002453 (Application date: 2008.04.30); Eun Kyung Noh, Sung Jae Na, Sujith S, Sang-Wook Kim, and Bun Yeoul Lee* J. Am. Chem. Soc. 2007, 129, 8082-8083 (2007.07.04); Sujith S, Jae Ki Min, Jong Eon Seong, Sung Jae Na, and Bun Yeoul Lee, Angew. Chem. Int. Ed., 2008, 47, 7306-7309 (2008.09.08)]. The catalyst developed by the present inventors shows high activity and high selectivity, and provides copolymers with a high molecular weight. Moreover, since the catalyst realizes polymerization activity even at high temperature, it is easily applicable to commercial processes. In addition, since the catalyst includes quaternary ammonium salts in the ligand, there is an advantage that it is possible to easily separate catalyst from copolymers after copolymerization of carbon dioxide/epoxide.
The present inventors closely analyzed the catalyst specially showing high activity and high selectivity compared to the others in the catalyst group of the above-mentioned patent application and found that the catalyst has an unusual and unique structure that nitrogen atoms of the salen-ligand are not coordinated with a metal but only oxygen atoms are coordinated with the metal. (see the following Structure 1, Sung Jae Na, Sujith S, Anish Cyriac, Bo Eun Kim, Jina Yoo, Youn K. Kang, Su Jung Han, Chongmok Lee, and Bun Yeoul Lee* “Elucidation of the Structure of A Highly Active Catalytic System for CO2/Epoxide Copolymerization: A Salen-Cobaltate Complex of An Unusual Binding Mode” Inorg. Chem. 2009, 48, 10455-10465).

Also, a method of easily synthesizing the ligand of the compound of the Structure 1 has been developed (Min, J.; Seong, J. E.; Na, S. J.; Cyriac, A.; Lee, B. Y. Bull. Korean Chem. Soc. 2009, 30, 745-748).
The high-molecular weight poly(alkylene carbonate) can be economically prepared by using the compound of the Structure 1 as the highly active catalyst. However, the poly(alkylene carbonate) itself has a limitation in application field. In order to overcome such limitations, technologies for manufacturing a block copolymer of poly(alkylene carbonate) and any other polymer commercially available in the art and/or precise control of molecular weights are required. In particular, physical properties and processability of a resin may be enhanced by forming cross-linked higher molecular weight polymer chains, thereby application field can be expanded.